Devices intended to generate electromotive forces are usually based on electromagnetic or electrochemical phenomena. So-called (although incorrectly) electrostatic generators or machines use processes which basically involve coulomb forces The former generally provide high currents at low voltages; the latter usually supply weak electric currents at very high voltages. Electrostatic machines played an important role in early discoveries in the field of electricity. Nowadays, they have been relegated to specific research or industrial uses, such as, for example, the supply of high voltages for particle accelerators and for separators or precipitators.
In 1766, Ramsden constructed an electrostatic friction generator in which electrification was achieved by means of friction between glass and leather impregnated with tin bisulphide. Volta, Holtz and Voss (Chappins, J., Lecons de Physique Generale, Vol. II, Gauthier--Villans, Paris 1920), at around the same time, manufactured electrical machines (also called at that time electrophori) taking as a basis the phenomenon of electrification by induction or "influence". In 1883, J. Whimshurst invented his ingenious electrostatic machine which was for many years preferred by scientists and which is still used today, albeit rarely. A major advance in the field of electrostatic generators was made by R. J. van der Graaf who designed the generator which bears his name and which is currently the one in most use, both in small and in large sizes. (More, A., Electrostatics and its applications. Wiley. New York 1973). The "peletron" is a modified Van der Graaf generator using a system which is similar to an endless belt. In the Oak Ridge (USA) laboratory there is a peletron coupled to a 25 MV accelerator. Modern generators are usually accommodated in hermetic chambers which are filled at high pressures with some suitable gas, such as F.sub.6 S, which prevents dielectric breakdown and the harmful effects of environmental humidity The generator which is proposed here can also operate in a hermetic enclosure and any chosen atmosphere and at the appropriate pressure. If the "coaxial" arrangement is adopted, which is one of those proposed, the external cylinder can act simultaneously as the container to be filled by the gas.
In the historical sequence of electrostatic generators, those which are proposed here have individual characteristics as set forth hereinbelow in greater detail. Various basic mechanisms are offered, based on electrifying contacts achieved by rolling, which avoids the mechanical restrictions inherent in friction. Rolling is proposed as a method of electrification and generation of voltages.
On the basis of rolling, various designs of electrostatic generator are proposed, i.e. designs of a device which situates accumulations of electrical charges of opposite sign at separate locations in space. Various proposed designs have a symmetrical configuration both in terms of the mechanical aspect and in terms of the aspect of electrical functionality, which constitutes an original element. As a non-exclusive example, mention should be made of the device in FIG. 3 if the same radius is given to all the cylinders. In the coaxial arrangement (FIG. 6) there is a certain mechanical symmetry in respect of the elements assigned to each charge, but symmetry in electrical functionality.
The coaxial design (FIG. 6) also offers the particular feature that the entire electric field generated by the device is confined within the physical limits of the device, avoiding losses and interferences.
The electrostatic generator proposed in the present specification has, among other features, the novelty of its design, the originality of its operation, the simplicity of its basic construction, the possibility of grouping its basic elements together in a modular fashion and its adaptability to different performance requirements or demands.
The generator proposed herein is called "triboelectric" because it is based on the so-called "triboelectric" properties of some materials and "rolling" because it benefits from the electrification produced by rolling in triboelectric materials.
"Triboelectrification" is the process by means of which, by placing two specific materials in surface contact, accumulations of electrical charges of respectively opposite signs are produced on said surfaces. The phenomenon originates in the transfer of electrons close to the surface from one material to the other. In order for triboelectrification to take place, it is not essential for one surface to cause friction on the other. If the triboelectrified media are insulating, the accumulations of charges will persist when there is no longer any contact between the surfaces of the media.
By trying out different pairs of materials, "triboelectric series" have been established, or rather ordered lists of materials which are positively electrified by contact with those which precede them and negatively electrified by contact with those which follow them. As an example, mention is made of that formulated by Montgomery and reproduced by W. Harper in his work "Contact and Rollingal Electrification" (Oxford, at the Clarendon Press, 1967): wool-nylon-cellulose-silk-cellulose acetate-methyl methacrylate-dacron-orlon-polyvinyl chloride-dynel-velon-polyethylene-teflon.